Why would I have to sign a contract like this?

I recently had to fill out paperwork to start substitute teaching at a preschool. I had to sign a contract saying that I will never talk on a cell phone while driving. Driving has nothing to do with teaching in a classroom so why would I have to sign something like this?
I should have asked the lady going through the paperwork with me, but she was rushing me so I could make it to take the drug test on time.